Re: [PATCH v5 00/12] mm/debug_vm_pgtable: Enhancements

From: Anshuman Khandual
Date: Tue Aug 03 2021 - 02:49:39 EST

On 8/2/21 11:34 AM, Gavin Shan wrote:
> There are couple of issues with current implementations and this series
> tries to resolve the issues:
> (a) All needed information are scattered in variables, passed to various
> test functions. The code is organized in pretty much relaxed fashion.
> (b) The page isn't allocated from buddy during page table entry modifying
> tests. The page can be invalid, conflicting to the implementations
> of set_xxx_at() on ARM64. The target page is accessed so that the
> iCache can be flushed when execution permission is given on ARM64.
> Besides, the target page can be unmapped and accessing to it causes
> kernel crash.
> "struct pgtable_debug_args" is introduced to address issue (a). For issue
> (b), the used page is allocated from buddy in page table entry modifying
> tests. The corresponding tets will be skipped if we fail to allocate the
> (huge) page. For other test cases, the original page around to kernel
> symbol (@start_kernel) is still used.
> The patches are organized as below. PATCH[2-10] could be combined to one
> patch, but it will make the review harder:
> PATCH[1] introduces "struct pgtable_debug_args" as place holder of all
> needed information. With it, the old and new implementation
> can coexist.
> PATCH[2-10] uses "struct pgtable_debug_args" in various test functions.
> PATCH[11] removes the unused code for old implementation.
> PATCH[12] fixes the issue of corrupted page flag for ARM64
> Changelog
> =========
> v5:
> * Pick r-bs from Anshuman and rebase to 5.14.rc4 (Gavin)
> * Use args->start_p4dp to free p4d entries (Anshuman)
> * Introduce helper to allocate huge page in init_arg() (Anshuman)
> * Bail early if the allocated page doesn't exist in
> swap_migration_tests() and correct the comments (Anshuman)
> * Add fixes tag to PATCH[v4 12/12] (Christophe)
> * Address misc comments (Anshuman)

Apart from the proposed changes discussed for the first patch [PATCH 1/12],
this series overall looks good now. It clears build tests on all supported
platforms. I was able to test this on arm64 and x86 platforms with various
functional config combinations. It would be still great if others can take
a look as well.

- Anshuman